It is a well-known practice for these devices to use shank hooks mounted to turn on multi-line pulley blocks through the intermediary of sprockets, i.e., thrust ball bearings.
In the most common embodiments, the hook, with or without a suspended load, is rotated manually when approaching the place where the load is gripped or deposited. Despite protective devices and safety measures, this type of operation always places the operator or worker at bodily risk, whether this risk involves handling moving parts or simply exists by virtue of his proximity to the load being handled.
In more elaborate known embodiments (for example, see French patent 1 229 282) the rotation of the hook or more generally of the load gripping device is driven by electric motor, and is remote-controlled from the control station located on the lifting device. For turret slewing cranes with a distribution boom, for example with distribution carriage and lifting cable forming a block and tackle, pulley blocks already exist having a remote-controlled back-geared motor to drive the turning hook for rotation. In this case, the electric feed and remote control cable for the motorization of the turning hook passes over a coiler placed on the load distribution carriage, such cable winding and unwinding on the coiler drum depending on the position of the carriage on the boom and the height under the hook. In these embodiments, two problems must be overcome, i.e., on the one hand, first maintaining sufficient mechanical tension on the feed and remote control cable and, second, protection against the risk of shearing and deterioration of the feed and remote control cable in event the lifting cables become twisted.
As recommended by published German Patent Application 3 234 395, the problems related to the feed and remote control cable can be solved by feeding the electric motor that drives the hook in rotation using a battery mounted on the pulley block body, and by using radio remote control. This known solution nonetheless requires that the battery be recharged frequently, i.e. every night.
Finally, to avoid recharging the battery, a motorized load rotation device has already been conceived having an "autonomous" power supply, i.e. the motorized load rotation device itself ensures the production, storage, restoration and renewal of the power it needs to operate, taking advantage of the movement of the lifting cable through the pulley block with respect to a pulley in the device, while loads are being handled and especially during raising and lowering movements. In this way, published Dutch Patent Application 7614360 proposes a mechanical transmission from at least one pulley to a hydraulic pump, and a hydraulic circuit with an accumulator that makes it possible to feed a hydraulic motor that drives the load in rotation. Such a hydraulic embodiment is expensive and is justified only when applied to lifting devices that handle very heavy loads, as is the case especially for container carrier cranes in ports. Such a device also presents other problems:
Its autonomy, related to the hydraulic accumulator capacity, is limited.
Its total mass is high, considering all of the necessary mechanical and hydraulic mechanisms, which detracts from the useful load of the lifting unit.
The hydraulic mechanism to set the load into rotation must be electronically controlled and monitored.
A separate electricity source is also needed for the remote control signal receiver.